|Publication number||US7366380 B1|
|Application number||US 11/109,210|
|Publication date||Apr 29, 2008|
|Filing date||Apr 18, 2005|
|Priority date||Apr 18, 2005|
|Publication number||109210, 11109210, US 7366380 B1, US 7366380B1, US-B1-7366380, US7366380 B1, US7366380B1|
|Inventors||Mark Peterson, Mark Harrison|
|Original Assignee||Luxtera, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (6), Non-Patent Citations (3), Referenced by (22), Classifications (7), Legal Events (5)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates to a planar lightwave circuit (PLC) for connecting optical fibers to the top of an optical or optoelectronic device or optical or optoelectronic integrated circuit and providing a low loss optical coupling between the fibers and the device or integrated circuit.
Optical fibers have been widely used for the propagation of optical signals, especially to provide high speed communications links. Optical links using fiber optics have many advantages compared to electrical links: very large potential bandwidth, high noise immunity, reduced power dissipation and minimal crosstalk.
Recent advances in the fabrication of silicon based optical and optoelectronic integrated circuits have resulted in the making of optical waveguides with submicron cross sectional dimensions. Fiber optic cables have typically been edge connected to the sides of optical and optoelectronic integrated circuits, but this method is not readily useable for connecting to submicron waveguides, because of the large mismatch in cross sectional dimensions between a typical SMF fiber core and a submicron waveguide. There have also been recent advances in the design and production of grating couplers to connect to submicron waveguides, which means that optical fibers could be connected to the top of an optical integrated circuit, if a suitable connector were available.
Planar lightwave circuit (PLC) connects optical fibers to the top of an optical or optoelectronic device or optical or optoelectronic integrated circuit. Light propagating through optical fibers is directed to optical waveguides disposed on optical devices. The optical fibers can be in the form of individual fibers, a fiber ribbon or a fiber array. Fiber optic cables can be plugged into a ferrule attached to the PLC. The PLC can also include optical components integrated into the optical path between the optical fibers and the optical device.
Connecting optical fibers 101, 102 and 103 directly to the side or edge of integrated circuit 120 can be accomplished if the optical fibers and waveguides are compatible in terms of physical and/or optical characteristics, such as (but not limited to) spacing, cross sectional areas and polarization characteristics. Various types of fibers, such as SMF, PMF or MMF, can be coupled to integrated circuit 120 using fiber array 110.
Fiber array 110 is not a practical solution for the edge coupling of optical fibers to integrated waveguides on integrated circuits if there is a large difference in cross sectional dimensions of the optical modes. Fiber array 110 cannot efficiently connect the typical SMF fiber core to the submicron core of a waveguide constructed on silicon or SOI. Fiber array 110 is also not useable if an optical fiber is to be connected to the top of an optical or optoelectronic integrated circuit while the fibers are horizontal, which is preferred in many practical mounting conditions.
Apparatus 250 also operates in the reverse direction, so that light from device 256 directed up towards surface 265 will be reflected into the core 261 of fiber 260.
One of the limitations of fiber to chip coupler 250 is the somewhat large distance between the core 261 of fiber 260 and device 256 on chip 255 resulting in a relatively large insertion loss for coupler 250.
Improved fiber to chip couplers using cut fibers positioned on the surface of a device are described in U.S. patent application Ser. No. 10/779,040, filed on Mar. 11, 2004 and entitled: “Fiber to Chip Coupler”, which is incorporated herein by reference.
PLC 300 provides a connection between an optical fiber (not shown in
The layer of adhesive can be any of a variety of adhesive materials, such as: an adhesive, an epoxy, solder or glass frit. PLC 300 has at least three surfaces: planar bottom side or base 301, left side 305 and planar angled reflective side 315. Surface 305 is preferably flat, but can in some applications be fabricated as a curved surface. Reflective coating 316 coats angled side 315. Various types of fibers, such as SMF, PMF or MMF, can be coupled to device 350 using PLC 300.
Reflective coating 316 can be made of a single layer or multiple layers. A single layer coating 316 can be made of materials such as: metal, dielectric or adhesive. A multilayer coating 316 can be made of several layers of metal, dielectric or adhesive. Various metals such as aluminum, nickel, chromium and gold can be used as a layer of coating 316. Reflective coating 316 can be designed and fabricated as a wavelength selective coating, so that only certain wavelengths of light are reflected at surface 315. Surface 315 and coating 316 are preferably smooth surfaces to maximize the reflection of light at surface 315.
Total internal reflection of light can occur at an uncoated surface 315, if the refractive index of PLC 300 is considerably higher than the refractive index of the air next to surface 315. Similarly, if surface 315 of PLC 300 is next to a medium other than air, then total internal reflection can occur at uncoated surface 315, if the refractive index of PLC 300 is considerably higher than the refractive index of the medium next to surface 315.
PLC 300 includes optical waveguide 310 surrounded by cladding layers. Waveguide 310 extends from surface 305 to the angled reflective surface 315 of PLC 300. Waveguide 310, as shown in
In other embodiments, PLC 300 can be fabricated with many optical waveguides similar to waveguide 310 and with the same optical port configuration: with one port at surface 305 and another port at angled reflective surface 315.
A light beam propagating through waveguide 310 towards angled reflective surface 315 is reflected down to optical component 355 on device 350. The light beam passes through bottom surface 301 of PLC 300, a thin layer of adhesive 330, top surface 351 and to component 355 of device 350. As is well known to those skilled in the art, the layers of adhesive between PLC 300 and device 350 should be uniform in thickness and have a refractive index that is equal or close to the refractive index of the bottom later of PLC 300 and the top layer of device 350. Before permanently fastening PLC 300 to optical device 350, the right hand port of waveguide 310 has to be optically aligned with optical component 355. Various optical alignment methods can be used, including a technique known as active alignment, and these methods are well known to those skilled in the art.
PLC 300 also operates in the reverse direction, such as when a light beam propagates upward from component 355 and is reflected by angled reflective surface 315 into waveguide 310, and then the light beam propagates toward the opposite end of waveguide 310 and towards surface 305.
Optical device 350 can have many devices or components on it, but in
Waveguide 310 of PLC 300 can be designed to match the cross sectional dimensions of an optical fiber edge coupled to waveguide 310 at surface 305. A light beam in waveguide 310 can be coupled to optical component 355 on device 350, and if component 355 is a grating coupler, the grating coupler can provide a coupling of the light beam to, for example, a submicron integrated waveguide on device 350. A suitably designed grating coupler can match the size of an optical mode propagating in waveguide 310. Grating couplers that can provide a transition in cross sectional area for a light beam are described in U.S. patent application No. 60/446,842 entitled “Optical Waveguide Grating Coupler” filed on Feb. 11, 2003, which is incorporated herein by reference.
A particularly advantageous aspect of the present invention is that PLC 300 can connect light from an optical fiber to devices on the top of device 350, where the fiber is edge coupled to surface 305 of PLC 300.
Another advantage of the present invention is the short distance between the point of reflection on surface 315 and optical device 350, resulting in reduced insertion loss. The relatively short travel distance means that there is less divergence and distortion of light 320 (shown in
A typical SMF fiber has a diameter of 125 microns with a core of 9 microns. A light beam reflected from the diagonally cut end of a standard SMF fiber placed on its side on top of an optical device, has to travel a distance of at least 63 microns from the center of the core of the fiber to reach the surface of an optical device. Light beam 320 reflected down from the center of waveguide 310 by surface 315, could, for example, travel a distance as short as 20 microns, resulting in much lower coupling loss as compared to a cut fiber placed on a device. A coupling made using a cut fiber on a device will experience much more insertion loss as compared to PLC 300 used as a connector between an optical fiber and an optical device.
PLC 300 also has the advantage of providing a mode size match between an optical mode propagating through an optical fiber and the mode size at the input of a grating coupler on the surface of an optical device.
Angled reflective surface 315 is at an acute angle with respect to the base 301 of PLC 300. This acute angle determines the angle at which light 320 traverses through surfaces 301 and 351 and into device 350. Surfaces 301 and 351 are typically parallel or substantially parallel planes. The angle of surface 315 relative to base 301 can be selected by those skilled in the art, in order to provide a useable angle for light beam 320 going through surfaces 301 and 351. If surface 315 is at a 45° angle with respect to base 301, then light beam 320 will be perpendicular to surfaces 301 and 351.
As shown in
When light beam 320 is directed up from device 350 to PLC 300 and towards angled reflective surface 315 within the area of the right hand port of waveguide 310, then light beam 320 is reflected by surface 315 into waveguide 310. When light beam 320 is directed up from device 350 at an acute angle, such as the exemplary 8° angle shown in
The end surface 305 of PLC 300 and the corresponding end surface of support block 340 are in the same plane and are preferably not perpendicular to the optical path through fiber stub 561 and waveguide 310, in order to minimize the reflection of light at surface 305. The surface 305 could, for example, have an angle of 8° with respect to the perpendicular to the optical path through the center of waveguide 310. In other embodiments, surface 305 can be perpendicular to the optical path through fiber stub 561 and waveguide 310. The shape of surface 305 is preferably planar, but can in other embodiments, have a curved or angled shape, with a profile to match a similarly shaped surface on ferrule 560.
If a connector assembly with an optical fiber is plugged into ferrule 560, and a light beam propagates down the optical fiber towards PLC 300, it will travel through fiber stub 561, waveguide 310, reflect off surface 315 and arrive at component 355 on device 350. The same optical path is followed in the reverse direction, if a light beam is directed up from component 355 on device 350 to PLC 300, and through to ferrule 560.
Package 600 is an example of a package for providing electrical connections between device 350 and external connections. Package 600 includes base 670, which is connected to device 350 by bonding wires 671. Base 670 includes bonding pads 672 and electrical leads 673. Many other electrical interconnection and package configurations are possible and well known to those skilled in the art. The electrical terminals or contacts 352 on device 350 can be any one of various well known types, such as: pads, bumps, solder balls and others that can be used for making electrical connections to a device or integrated circuit.
Package base 670 is one example of a means of electrical interconnection between device 350 and external electrical connections.
Package base 670 includes wire bonding pads 672 and electrical leads 673. Bonding wires 671 provide electrical connections between device 350 and base 670. Wires 671 are attached between device pads 352 and base pads 672. Electrical leads 673 on package 600 can be attached to a printed circuit board or connected to a socket. Only a few electrical connections to device 350 are shown in
The polished ends of fibers 681 and 683 which connect to ferrule 560 and the corresponding polished ends of fiber stubs 561 and 563 are preferably not perpendicular to the optical path through the fibers 681 and 683 and the fiber stubs 561 and 563, in order to minimize the reflection of light at the polished ends. The polished ends could, for example, have an angle of 8° with respect to the perpendicular to the optical path through the fibers. In other embodiments, the polished ends of fibers 681 and 683 and the corresponding polished ends of fiber stubs 561 and 563 can be perpendicular to the optical path through the fibers 681 and 683 and the fiber stubs 561 and 563.
In alternate embodiments of the present invention, ferrule 560 can be configured with alignment holes and connector assembly 680 can be configured with alignment pins.
A particularly advantageous aspect of the present invention as shown by package 600 in
Package 700 is another example of a package for providing electrical connections between device 350 and external connections. Package 700 includes base 790, which is connected to device 350 by a group of bonding wires 791. Base 790 includes many bonding pads 792, conductors 793 and BGA contacts 794.
The components on device 350, which require electrical connections to off-chip signal paths and devices are connected to base 790 by each of the group of electrical bonding pads 352 and each of the group of bonding wires 791. BGA contacts on package 700 can be attached to a printed circuit board or connected to a socket.
Each of the BGA contacts 794 is connected to one or more of the bonding pads 352 on device 350 by one of the bonding wires 791, one of the bonding pads 792 and one of the conductors 793. Base 790 can be made of a single layer or multi-layer substrate. Conductors 793 can be copper or other metal conductive paths or traces, positioned on the top surface, the bottom surface or within an intermediate layer of base 790. Conductors 793 on a lower layer can be connected to each of their BGA contacts 794 by conductive vias. Each BGA contact on base 790 can be connected to one or more electrical bonding pads 352 on device 350 in a similar manner.
Only a few electrical connections to device 350 are shown in
The cover to package 700 is not shown in
The elements of
A particularly advantageous aspect of the present invention as shown by package 700 in
A particularly advantageous aspect of this embodiment of the present invention is the packaging of the pigtail and the connector together into one assembly for quick installation.
One optical fiber 961 is visible in
A particularly advantageous aspect of this embodiment of the present invention is the packaging of a fiber array and a connector together into one assembly for quick installation.
PLC 1000 can include many optical components and optical waveguides where the optical waveguides are used to connect the internal optical components, such as 1011, to external optical fibers and to an optical device, such as 350 in
Waveguides 1010 and 1012, as shown in
A particularly advantageous aspect of the present invention is the integration of optical components and waveguides in a PLC to connect optical fibers to the top of an optical or optoelectronic device or integrated circuit.
PLC 1100 is positioned on top of device 350 and support block 340. A portion of the bottom surface of PLC 1100 is attached to the top surface 351 of device 350 by adhesive. PLC 1100 has at least three surfaces: planar bottom side or base 301, left side 1105 and planar angled reflective side 315. Surface 1105 is preferably flat, but can in some applications be fabricated as a curved surface. Reflective coating 316 coats angled side 315. Various types of fibers, such as SMF, PMF or MMF, can be coupled to device 350 using PLC 1100.
Waveguide 310, as shown in
The elements of
In alternate embodiments of the present invention, PLC 1100 can be configured with alignment holes and a mating connector assembly, similar to connector assembly 680 shown in
A particularly advantageous aspect of the present invention is the use of guide pins or alignment holes integrated into the PLC, which can then be mated with a variety of connector assemblies.
PLC 1200 includes optical waveguides 1210, 1211 and 1212 surrounded by layers of cladding. Waveguides 1210, 1211 and 1212 extend from surface 1205 to angled reflective surface 1215 of PLC 1200. The waveguides in
As shown in
PLC 1200 with its fan-in configuration is particularly advantageous in coupling a fiber array or a group of fibers to components on chip 1250, where the optical ports of the components on chip 1250 are separated apart from each other a smaller distance, than the spacing of the fibers connected to side 1205. For light propagating from right to left in
In other embodiments of the PLC of the present invention, the spacing between the waveguides at surface 1205 can be wider than the spacing at angled reflective surface 1215. Such an arrangement of waveguides would provide a “fan-out” capability to such a PLC, for light propagating from left to right in
Waveguides 1313 and 1314 in
Waveguide 1312 is a tapered waveguide extending from surface 1305 to angled surface 1315, which can modify the size and shape of an optical mode propagating through the waveguide. In other embodiments, a waveguide in a PLC of the present invention can be designed with a taper determined by a mathematical equation, such as an elliptical, hyperbolic, sinusoidal or other function.
Light propagating through waveguides 1312, 1313 and 1314 is reflected at respective areas of reflection 1322, 1323 and 1324.
Waveguides 1310 and 1311 extend from surface 1305 to optical device 1325 and waveguide 1316 extends from device 1325 to angled surface 1315. Waveguides 1310 and 1311 are in a fan-in configuration in
PLC 1300 with its fan-in, fan-out and optical mode shaping waveguide configurations is particularly advantageous in coupling a fiber array or group of fibers to components on chip 1350, where the optical ports of the components on chip 1350 have various port sizes and shapes and are separated apart from each with a variety of spacing distances.
As mentioned previously, the present invention has many particularly advantageous aspects, including that a PLC of the present invention provides a low loss connection, which can connect optical fibers to optical or optoelectronic devices on the top surface of an optical or optoelectronic device or integrated circuit. The short distance between the point of reflection on the angled reflective surface and the top of a device or integrated circuit makes low loss connections possible between the reflective surface of the PLC and an optical or optoelectronic device or integrated circuit. Also contributing to the low loss is the good mode size match between the waveguide in the PLC and a grating coupler on the device or integrated circuit. As mentioned previously, one advantage of the embodiment with the ferrule shown in
There are many other advantages to the present invention, such as: supporting high speed optical and electronic connections, high reliability, low cost compared to other solutions, compact design and high thermal conductivity of the package.
Although the present invention has been described in detail, it should be understood that various changes, substitutions and alterations can be made without departing from the spirit and scope of the invention.
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|International Classification||G02B6/42, G02B6/26|
|Cooperative Classification||G02B6/4249, G02B6/4214, G02B6/421|
|Apr 18, 2005||AS||Assignment|
Owner name: LUXTERA, INC., CALIFORNIA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:PETERSON, MARK;HARRISON, MARK;REEL/FRAME:016493/0039
Effective date: 20050225
|Jun 17, 2009||AS||Assignment|
Owner name: SILICON VALLEY BANK, CALIFORNIA
Free format text: SECURITY AGREEMENT;ASSIGNOR:LUXTERA, INC.;REEL/FRAME:022835/0340
Effective date: 20090615
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|Nov 7, 2011||FPAY||Fee payment|
Year of fee payment: 4
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Year of fee payment: 8